Major improvements to spack create (#2707)

* Initial changes to spack create command

* Get 'spack create <url>' working again

* Simplify call to BuildSystemGuesser

* More verbose output of spack create

* Remove duplicated code from spack create and spack checksum

* Add better documentation to spack create docstrings

* Fix pluralization bug

* Flake8

* Update documentation on spack create and deprecate spack edit --force

* Make it more obvious when we are renaming a package

* Further deprecate spack edit --force

* Fix unit tests

* Rename default template to generic template

* Don't add automake/autoconf deps to Autotools packages

* Remove changes to default $EDITOR

* Completely remove all traces of spack edit --force

* Remove grammar changes to make the PR easier to review